1. Field of the Invention
The present invention relates to silane coupling agents, methods for their preparation, and their use in rubber applications. More particularly, these silanes embody a new concept whose focus is to transform the hydrolysable group, once released from the silane, from a waste product to one that contributes to improvements in the processability and properties of the final product.
2. Description of Related Art
A large body of art exists relating to the composition, preparation, and uses of polysulfide silanes and mercaptosilanes in rubber and other applications. There is sufficient interest in this field that many of the original patents have begun to expire as new patents continue to appear. Most of the interest has centered around the sulfur functionality of these molecules. For example, there is a great number of patents dealing with mixtures of polysulfide silanes containing subtle variations in the sulfur rank distributions (i.e., variations in the value of x and in the distributions of the corresponding molecular species, in Formulae 1 and 2, below). Fewer, but nevertheless a sizeable number, of the citations also focus on variations in the linking group between sulfur and silicon.
On the other hand, very little attention has been focused on the hydrolysable portion of the molecule beyond attempts at broad coverage of alkoxy groups and in some cases other hydrolysable functionality, usually containing a single, but broadly defined, hydrocarbon group when, in fact, all that was of real interest has been ethoxy and, in some more recent cases, siloxy. Moreover, the hydrolysable group has been implicitly treated as an expendable portion and tolerated as an ultimate waste product of the molecule because it is lost during the process of using these silanes in their intended application.
U.S. Pat. No. 5,116,886 discloses a two-stage method for the surface modification of natural or synthetic, oxide or silicate fillers using certain organosilicon compounds of a given formula, wherein the filler and compound are intensively mixed without the addition of further solvents and homogenized mixture is subjected in a a preheated mixer to the hydrophobing reaction.
EP 0 631 982 A2 discloses aggregates comprised of particles that contain silicon dioxide, elastomers reinforced therewith, and tires having treads composed of such reinforced elastomers.